The present invention relates to flat panel television displays.
Since the early days of television, researchers have sought for a "picture on the wall" as an alternative to both television picture tubes and TV projectors. Presumably, the ideal embodiment would be a thin television set, either large or small, with the appearance of a painting in a frame but showing television pictures in full color.
It was recognized from the outset that to replace the scanning electron beam of the picture tube as a means for gaining separate access to the elements of the picture, separate electrical connections to all of the picture elements are necessary. The display panel must thus be divided into a matrix of discrete display elements, and connections must be made to each of these elements. As used herein, a bistable element is one in which the element has both a stable "on" and a stable "off" condition; one bistable element is an AC plasma element including a sealed envelope containing a suitable gas fill material and a pair of electrodes which are insulated from the gas fill. In certain cases, a DC plasma element may operate in a bistable manner.
In recent years several matrix panel display systems have been developed. One system is described in the publication "A Field-Interlaced Real-Time Gas-Discharge Flat Panel Display with Gray Scale", 1972 IEEE Conference on Display Devices Conference Record, New York City, October 11-12, 1972, pp. 70-75, by Y. S. Chen and H. Fukui. Another system is described in the publication "Good Quality TV Pictures Using a Gas-Discharge Panel," 1972 IEEE Conference on Display Devices Conference Record, New York City, October 11-12, 1972, pp. 77-82, by G. J. Chodil, M. C. DeJule, and J. Markin.
These two publications describe TV displays using DC plasma panels which are made by Burroughs Corporation and known by the trademark Self-Scan in which pictures are generated a TV line at a time with pulses of light emitted for about 50 microseconds for a standard TV display, 30 times/sec, thereby giving a duty factor of 0.0015. As used herein duty factor is defined as the ratio of the time in which a cell emits light during one picture frame to the time period for one picture frame.
Another system is described in the publication "Picture Display with Gray Scale in the Plasma Panel," 1973 SID International symposium Conference Record, New York City, May 15-17, 1973, pp. 70-71 by S. Umeda, K. Murase, H. Ishizaki and K. Jurahashi. A fourth system is described in the publication "Plasma Display with Gray Scale, " 1973 SID International Symposium Conference Record, New York City, May 15-17, 1973, pp. 72-73 by K. Jurahashi, H. Tottori, F. Isogai and N. Tsuruta. The third and fourth publications describe TV displays using AC plasma panels, which are similar to those manufactured by Owens-Illinois Company, in which pictures are generated with pulses of light lasting considerably more than a single TV line period through use of the inherent image storage capabilities of the AC plasma panel. In the third publication, some measure of gray scale is achieved through the use of a group of four cells to form each resolution element of the display. These cells supply one, two, four and eight units of brightness, respectively and are operated in the digitized slow-scan TV like signals. In the fourth publication, gray scale is achieved with each cell turned on for four different intervals of time, these intervals being of one, two, four and four times a unit duration, the unit being large enough to provide a high duty factor.
The methods which have been used for line-at-a-time matrix TV display, such as described in the first and second publications, impose a low duty factor on the display, requiring that the instantaneous brightness be orders of magnitude greater than the average brightness level perceived by the viewer.
The two methods previously used with AC plasma panels, such as those described in the third and fourth publications, provide greatly increased duty factor through the use of inherent storage capabilities in the panel (i.e., bistable operation of each cell), but this advantage is accomplished at a serious loss in the number of gray scale levels in both systems. In addition, there is loss of picture resolution in the third system because four, separate cells form each resolution element. In the fourth system, there is considerable flicker of the picture and reduction by half in the vertical resolution.